1. Field of the Invention
The present invention relates to an imaging lens used for an in-vehicle camera or a monitoring camera using an imaging device, such as a CCD or a CMOS, and more particularly, to an imaging lens used for an in-vehicle camera that captures the images of the front, side, and rear of a vehicle.
2. Description of the Related Art
In recent years, the size of an imaging device, such as a CCD or a CMOS, has been reduced, and the number of pixels thereof has increased. Therefore, it is necessary to reduce the size and weight of an imaging apparatus body and an imaging lens provided therein. Meanwhile, for example, in-vehicle cameras or monitoring cameras require a high-performance and inexpensive lens that has high weather resistance, that can be used in a wide temperature range in a vehicle from a low temperature in a cold region to a high temperature in a tropical region, and that has such a small F number that it can be used at night.
For example, Japanese Patent No. 3723654, JP-A-2003-329925, JP-A-10-293246, JP-A-2002-277734, JP-A-2002-228925, JP-A-03-063613, and JP-A-2008-008960 disclose imaging lenses that meet the requirements. The disclosed imaging lenses each have a five-lens optical system including a relatively small number of lenses.
However, in the imaging lenses, with an improvement in the performance of an imaging device used for an imaging apparatus, it is necessary to reduce the size and manufacturing costs of the imaging lens and improve the brightness thereof. However, in the optical system according to the related art, it is difficult to achieve a small, fast, and inexpensive imaging lens capable of meeting the requirements.